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    <td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">Compile 
      Time Configuration</font></b></font></td>
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<p><b><a name="compiletime_config"></a>Library compile time configuration</b></p>
<P dir="ltr">The C++ preprocessor iterator library may be configured at compile 
  time by specifying different preprocessor constants to include different additional 
  features. The possible preprocessor constants are described in the following 
  table. </P>
<table width="100%" border="0" align="center">
  <tr> 
    <td colspan="2" class="table_title"><b>Summary of possible preprocessor constants 
      for<br>
      library configuration</b></td>
  </tr>
  <tr> 
    <td width="46%" class="table_cells"><code>BOOST_WAVE_SUPPORT_WARNING_DIRECTIVE</code></td>
    <td width="54%" class="table_cells"> <p>Support the <span class="preprocessor">#warning</span> directive</p></td>
  </tr>
  <tr> 
    <td width="46%" class="table_cells"><code>BOOST_WAVE_SUPPORT_MS_EXTENSIONS</code></td>
    <td width="54%" class="table_cells"> <p>Support several MS specific language 
        extensions (i.e. <tt>__int8</tt> et.al.)</p></td>
  </tr>
  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_PREPROCESS_ERROR_MESSAGE_BODY</code></td>
    <td class="table_cells"><p>Enable the preprocessing of the message bodies 
        of <span class="preprocessor">#error</span> and <span class="preprocessor">#warning</span> 
        directives.</p></td>
  </tr>
  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_EMIT_PRAGMA_DIRECTIVES</code></td>
    <td class="table_cells"><p>If defined, then the <span class="preprocessor">#pragma</span> 
        directives are returned as a token sequence to the caller, if not defined, 
        the whole <span class="preprocessor">#pragma</span> directive is skipped. </p></td>
  </tr>
  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_PREPROCESS_PRAGMA_BODY</code></td>
    <td class="table_cells"><p>Enable the preprocessing of the bodies of all <span class="preprocessor"> 
        #pragma</span> directives.<br>
        Note though, that the body of an <tt>operator&nbsp;_Pragma()</tt> is always preprocessed as this is required by the C99 Standard <a href="references.html#iso_c">[2]</a>. 
      </p></td>
  </tr>
  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_ENABLE_COMMANDLINE_MACROS</code></td>
    <td class="table_cells"><p>Enable the functionality required to define macros 
        with the command line syntax (-DMACRO(x)=definition)</p></td>
  </tr>
  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_STRINGTYPE</code></td>
    <td class="table_cells"><p>The tokens generated by the <tt>Wave</tt> library 
        contain the token data and the file position, where this token was found 
        in the input stream. <br>
        This constant may be used to redefine the data type, which is used to 
        hold the token data and the corresponding file name. If this isn't defined 
        it defaults to std::string. (The here defined data type should be compatible 
        to the std::string type)</p></td>
  </tr>
  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_VARIADICS_PLACEMARKERS</code></td>
    <td class="table_cells"><p>If defined, then the preprocessor library supports 
        variadics and placemarkers. Note, to support C99 mode, this constant must 
        be defined too.</p></td>
  </tr>
<tr> 
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_CPP0X</code></td>
    <td class="table_cells"><p>If defined, then the preprocessor library supports 
        C++0x keywords and C++0x specific features, such as variadics, placemarkers, extended character and string literals. This implies the definitions of the <code>BOOST_WAVE_SUPPORT_VARIADICS_PLACEMARKERS</code> constant.</p></td>
  </tr>  <tr>
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_CPP1Z</code></td>
    <td class="table_cells"><p>If defined, then the preprocessor library supports
        C++17 keywords - currently just <code>__has_include</code>. It implies <code>BOOST_WAVE_SUPPORT_CPP0X</code>.</p></td>
  </tr>
  </tr>  <tr>
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_CPP2A</code></td>
    <td class="table_cells"><p>If defined, then the preprocessor library supports
        C++20 keywords, specifically <code>__VA_OPT__</code>. It implies <code>BOOST_WAVE_SUPPORT_CPP1Z</code>.</p></td>
  </tr>
  </tr>  <tr> 
    <td class="table_cells"><code>BOOST_WAVE_MAX_INCLUDE_LEVEL_DEPTH</code></td>
    <td class="table_cells"><p>If defined, it will determine the initial maximal 
        possible include file nesting depth supported. It defaults to 1024.</p></td>
  </tr>
  <tr>
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_PRAGMA_ONCE</code></td>
    <td class="table_cells"><p>If defined, then the <code>#pragma once</code> directive is supported by <tt>Wave</tt>. This specifies that the file, in which the pragma resides, will be included 
      (opened) only once by the compiler in a build. </p></td>
  </tr>
  <tr>
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_PRAGMA_MESSAGE</code></td>
    <td class="table_cells"><p>If defined, then the <code class="preprocessor">#pragma message(&quot;&quot;)</code> directive is supported by <tt>Wave</tt>. This pragma simply generates a remark cotaining the message text. The body of the #pragma message is preprocessed whenever the <code><code>BOOST_</code>WAVE_PREPROCESS_PRAGMA_BODY</code> constant is defined as well . </p></td>
  </tr>
  <tr>
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_INCLUDE_NEXT</code></td>
    <td class="table_cells"><p>If defined, then the <code>#include_next</code> directive is supported by <tt>Wave</tt>. This is syntactically equivalent to the <code class="preprocessor">#include</code> directives, but may be used to inherit a header file (i.e. to include a file, which is named as the current file containing the <code>#include_next</code>).</p></td>
  </tr>
  <tr>
    <td class="table_cells"><code>BOOST_WAVE_USE_STRICT_LEXER</code></td>
    <td class="table_cells"><p>If this is defined to something != 0, then the C/C++ lexers recognize the 
      strict C99/C++ basic source character set. If it is not defined or defined 
    to zero, the lexers recognize the <span class="string">'$'</span> character as part of identifiers.</p></td>
  </tr>
  <tr>
    <td class="table_cells"><code>BOOST_WAVE_PRAGMA_KEYWORD</code></td>
    <td class="table_cells"><p>If this is defined to a string literal it will be used as the pragma keyword recogniyed by the library as specific Wave pragmas. This constant defaults to <span class="literal">&quot;wave&quot;</span>, i.e. the library recognizes all      <span class="preprocessor">#pragma wave option [(argument)]</span>  directives and dispatches the handling to the interpret_pragma() preprocessing hook function (see: <a href="class_reference_ctxpolicy.html">Preprocessing Hooks</a>). The arguments part of the  pragma is optional.<br>
      </p>    </td>
  </tr>
  <tr>
    <td class="table_cells"><code>BOOST_WAVE_SUPPORT_LONGLONG_INTEGER_LITERALS</code></td>
    <td class="table_cells"><p>The C++ standard requires the preprocessor to use one of the following 
      types for integer literals: <code>long</code> or <code>unsigned long</code> depending on a optional 
      suffix (<span class="literal">'u'</span>, <span class="literal">'l'</span>, <span class="literal">'ul'</span>, or <span class="literal">'lu'</span>). Sometimes it is required to preprocess integer literals larger than that
        (i.e. <code>long long</code> or <code>unsigned long long</code>). Defining this pp constant enables the recognition of long long integers
even if these do not have the <span class="literal">'ll'</span> suffix.</p>
      <p>This preprocessor constant is effective only, if your target platform supports 
        long long integers (<code>BOOST_HAS_LONG_LONG</code> is defined). Please note, that this setting doesn't relate to the Wave support option
        <code>support_option_long_long</code>, which enables the recognition of <span class="literal">'ll'</span> suffixes 
        only.
    </p>
      </td>
  </tr>
    <tr>
        <td class="table_cells">
            <code>BOOST_WAVE_SUPPORT_THREADING</code></td>
        <td class="table_cells">
            <p>This preprocessor constant allows to configer whether the Wave library will be built
                with threading support enabled or not. This value (if defined) should be set to
                zero ('0') if threading needs to be disabled and to a numerical value not equal
                to zero, if threading should be enabled explicitly.
            </p>
            <p>
                If this constant is not defined, the Wave library will be built using the threading
                as picked up from the Boost build environment (see <code>BOOST_HAS_THREADS</code> in the Boost
                    configuration dosumentation).</p>
        </td>
    </tr>
</table>
<P dir="ltr"><b><a name="using_custom_lexer"></a>Using a different token type or lexer type in conjunction with Wave </b></P>
<P dir="ltr">It is possible to use the <tt>Wave</tt> library while using your own token and/or lexer types. This may be achieved by providing your lexer type as the second template parameter while instantiating the <tt>boost::wave::context&lt;&gt;</tt> object. The token type used by the library is derived from the <tt>token_type</tt> typedef to be provided by the lexer type. If you want to provide your own token type only, you may use the <tt>boost::wave::lex_iterator&lt;&gt;</tt> type contained with the library. This type needs to be parameterized with the token type to use. </P>
<P dir="ltr">The <tt>Wave</tt> library contains several samples illustrating these possibilities. The <tt>cpp_tokens</tt> sample shows the usage of a custom lexer and a custom token types. The lexer type used is functionally fully compatible to the <tt>re2c</tt> <a href="references.html#re2c">[3]</a> based lexer used by default. It is implemented based on the <tt>SLex</tt> <a href="references.html#slex">[5]</a> lexer example written by Dan Nuffer. The token type used therein is functionally equivalent to the default token type except for an additional <tt>operator&lt;&lt;</tt> used for dumping the information carried by the token.</P>
<P dir="ltr"><b><a name="compilation_models"></a>Separation and inclusion compilation 
  models</b></P>
<P dir="ltr">The <tt>Wave</tt> C++ preprocessor iterator library is build almost 
  completely as a header only library (except for the re2c based lexer). If you're 
  trying to include all required files at once you will mention, that the resulting 
  compilation times are very large (up to an hour - depending on your system configuration). 
  This straightforward method we'll call the inclusion compilation model. If you 
  do not pay attention to compilation times, that's the way to go, no special 
  handling is needed.</P>
<P dir="ltr">If you're interested in decreasing compilation times, the following 
  method is to be used. This we will call it the separation compilation model. 
  The trick is to separate the different objects such, that they are compilable 
  separately. The function, which instantiates the templated object in question 
  is factored out such, that its definition is visible to only one translation 
  unit. To simplify this further this creation function is packaged into a small 
  generator template structure.</P>
<P dir="ltr">There are two levels of separation implemented: the separation of 
  the compilation of the C++ lexer and the separation of the compilation of the 
  different Spirit grammars used. To use these separations you will have to define 
  two preprocessor constants while compiling the whole application and you will 
  have to explicitly instantiate some helper templates. The following tables
  shows these constants in detail.</P>
<table width="90%" border="0" align="center">
  <tr> 
    <td colspan="2" class="table_title"><b>Summary of possible compilation constants 
      required <br>
      to enable the separation compilation model</b></td>
  </tr>
  <tr class="table_title"> 
    <td width="25%"><b>Separate</b></td>
    <td width="75%"><p><code><font face="Verdana, Arial, Helvetica, sans-serif">Preprocessor 
        constant</font></code></p></td>
  </tr>
  <tr> 
    <td width="25%" class="table_cells"><code>C++ lexer</code></td>
    <td width="75%" class="table_cells"> <p><code><code>BOOST_</code>WAVE_SEPARATE_LEXER_INSTANTIATION</code></p></td>
  </tr>
  <tr> 
    <td width="25%" class="table_cells"><code>Spirit grammars</code></td>
    <td width="75%" class="table_cells"> <p><code><code>BOOST_</code>WAVE_SEPARATE_GRAMMAR_INSTANTIATION</code></p></td>
  </tr>
</table>
<P dir="ltr">The following table shows the explicit template instantiations required, 
  if you want to use the separation compilation model. The <tt>TokenT</tt> placeholder 
  type has to be replaced with your token type to use and the <code><tt>LexIteratorT</tt></code> placeholder type has to be replaced with your lex iterator type you've used while instantiation of the <tt>boost::wave::context&lt;&gt;</tt> object. You will achieve the best 
  results, if you place these into separate compilation units each. The <tt>IteratorT</tt> 
  placeholder should be replaced by the iterator type, which was used to instantiate 
  the <tt>boost::wave::context&lt;&gt;</tt> object.</P>
<table width="90%" border="0" align="center">
  <tr> 
    <td colspan="2" class="table_title"><b>Summary of required explicit template 
      instantiations <br>
      required when using the separation compilation model</b></td>
  </tr>
  <tr class="table_title"> 
    <td width="25%"><b>Separate</b></td>
    <td width="75%"><p><code><font face="Verdana, Arial, Helvetica, sans-serif">Templates 
        to explicitly instantiate</font></code></p></td>
  </tr>
  <tr> 
    <td width="25%" class="table_cells"><code>C++ lexer</code></td>
    <td width="75%" class="table_cells"> <code><span class="keyword">template</span> 
      cpplexer::re2clex::new_lexer_gen&lt;<tt>IteratorT</tt>&gt;;</code></td>
  </tr>
  <tr> 
    <td width="25%" class="table_cells"><code>Spirit grammars</code></td>
    <td width="75%" class="table_cells"> <p><code><span class="keyword">template</span> wave::grammars::expression_grammar_gen&lt<tt>TokenT</tt>&gt;;<br>
        <span class="keyword"> template</span> wave::grammars::intlit_grammar_gen&lt;<tt>TokenT</tt>&gt;;<br>
        <span class="keyword"> template</span> wave::grammars::chlit_grammar_gen&lt;<tt>TokenT</tt>&gt;;<br>
        <span class="keyword"> template</span> wave::grammars::cpp_grammar_gen&lt;<tt>LexIteratorT</tt>&gt;;<br>
        <span class="keyword"> template</span> wave::grammars::predefined_macros_grammar_gen&lt;<tt>LexIteratorT</tt>&gt;;<br>
    <span class="keyword"> template</span> wave::grammars::defined_grammar_gen&lt;<tt>LexIteratorT</tt>&gt;;</code></p></td>
  </tr>
</table>
<p>To see an example of this you can look at the <tt>Wave</tt> driver program 
  included as an acompanion sample to the C++ preprocessor iterator library. The 
  corresponding files are named obviously <span class="string">&quot;instantiate_...something.cpp&quot;</span>, 
  where the <span class="string">'...somthing'</span> is a hint, which grammars 
  are explicitly instantiated inside. By using the separation model the compilation
  times required to build the <tt>Wave</tt> example are dropped by up to 90%.</p>
<P dir="ltr"><b><a name="compiler_requirements"></a>Compiler Requirements</b></P>
<p>Beginning with version 1.77, Wave will require building with C++11 features, and will no longer support the use of older compilers. However, Wave will continue to <em>emulate</em> the features of older preprocessors indefinitely.<p>
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<p class="copyright">Copyright &copy; 2003-2011 Hartmut Kaiser<br>
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<font size="2">Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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